1. They are both childlike. While Scout matures greatly throughout the novel, she still maintains an inquisitive nature, just likes Boo's childish curiosity (only he practices his from the shelter of his house).
2. They already "know" each other before they meet in person. Boo has observed the children and is most likely amused by their antics. He communicated with them through the knothole in the tree, and Scout knew from that point on that Boo was not evil or scary.
3. At the novel's end, Scout has learned to be tolerant and to recognize people for who they really are. When she meets Boo, she is ready to begin practicing her dad's admonition to "climb into someone else's skin and walk around in it."
Throughout the novel, Scout muses at the possibility of one day meeting her reclusive neighbor. She even imagines that she would have a typical friendly conversation about the weather with Boo Radley as she randomly walks past his home. Boo Radley has always kept a close watch on Scout and her brother as they played throughout the neighborhood. He has expressed his friendship by placing gifts in the knothole of his tree. Needless to say, Boo is very familiar with the children. At the end of the novel, Scout meets Boo for the first time while Jem recovers from Bob Ewell's attack. Scout grabs Boo's hand and takes him to the front porch before walking him home. The two characters seem to be instant friends because Boo has been keeping an eye on Scout. Both characters have had positive experiences with each other, and there is a mutual understanding between them when they first meet.
At first Scout views Boo as some kind of myth as if he does not really exist, yet as she grows older she realizes how wrong it was for her to judge him. Boo understands the children are not evil as he leaves little presents within the tree, but his brother soon closes up the hole so he cannot send gifts. In the end he helps save the children. When Scout realizes the importance of her father telling her about how you should not easily judge someone, but in fact you should understand their position as she does with Boo.